A 54-year-old female was being assessed for thyroid dysfunction following self-reported symptoms of weight gain and lethargy. The patient had no neck tenderness and exhibited no symptoms of goiter. Past medical history was significant for relapsing-remitting multiple sclerosis and anxiety. Laboratory investigations were ordered and the results were consistent with thyrotoxicosis: thyroid-stimulating hormone (TSH) of 0.08 mU/L (reference range 0.34–4.82 mU/L), free thyroxine (FT4) of 33.2 pmol/L (10.0–20.0 pmol/L), and free triiodothyronine (FT3) of 46.1 pmol/L (3.5–6.5 pmol/L). Given that these laboratory values were not supported by the clinical presentation, new blood work was ordered. When a similar pattern of values was found (TSH 0.01 mU/L, FT4 > 103.0 pmol/L, FT3 > 46.1 pmol/L), a referral was made to endocrinology. Upon being questioned by the endocrinologist, the patient described taking high-dose biotin for her multiple sclerosis. The patient was advised to stop the biotin for 1 week before repeat testing. Follow-up blood work revealed the patient to be euthyroid, with a TSH level of 1.78 mU/L, FT4 of 12.6 pmol/L, and FT3 of 3.7 pmol/L, along with an undetectable TSH receptor antibody titre.

Clinical and commercial use of biotin

Biotin, also known as vitamin B7 or vitamin H, is a water-soluble vitamin that serves as a cofactor for a number of carboxylase reactions, making it essential to the functioning of various metabolic pathways.[1-4] It is involved in fatty acid synthesis, catabolism of branched-chain amino acids, gluconeogenesis, islet cell gene expression, insulin secretion, and the Krebs cycle.[4] The recommended dietary reference intake for biotin is 30 µg/day. The vitamin is found in various foods, including egg yolk, pork, liver, whole cereals, soybeans, avocado, cauliflower, and leafy greens.[1-4] Because of its abundance in a typical North American diet, biotin deficiency is uncommon, and supplementation is rarely indicated. Clinically, biotin may be prescribed in patients with malabsorptive disorders or in those on total parenteral nutrition. It may also be useful in relieving muscle cramps in hemodialysis patients.[5] High doses of biotin (5 to 30 mg/day) are recommended in certain inborn errors of metabolism, such as in biotinidase deficiency, propionic acidemia, or in holocarboxylase synthetase disorders.[6] More recently, mega-doses of biotin (up to 300 mg/day) have shown promise in secondary progressive multiple sclerosis.[7]

In the past decade, biotin supplementation in doses up to 20 mg a day has been marketed to promote hair, skin, and nail growth. Although there is limited evidence to support this claim, marketing led to biotin sales of up to 49.6 million units in the US alone between July 2016 and July 2017.[1] Biotin is currently the top- selling multivitamin supplement on Amazon.ca. Locally, a survey of 660 patients visiting the Diamond Health Care Centre Outpatient Laboratory at Vancouver General Hospital found that 50 respondents (7.6%) were taking biotin. The majority of users were female (92%) and biotin users tended to be younger than non-users: age 49 (19 to 85) years versus age 54 (19 to 98) years. The prevalence of biotin supplementation in our survey population was similar to that reported by the Mayo Clinic, which found 7.7% of outpatients to be ingesting biotin.[1]

Biotin interference with laboratory tests

As biotin is readily available over the counter and is perceived to be harmless, patients may not disclose their biotin use to physicians unless specifically asked. Further, health care providers may also view biotin supplementation as innocuous. However, when found in high concentrations in blood, biotin can interfere with laboratory tests that employ biotin-streptavidin interactions as part of the assay technology. Biotin-streptavidin binding is commonly used in immunoassays due to its avidity and stability, which facilitate immunoassay sensitivity and specificity. A 2017 study by Holmes and colleagues found that out of the 374 methods operated by 8 of the most popular immunoassay analyzers in the US, 221 (59%) were biotin-based.[4] Depending on the laboratory and the analytical platforms used, a broad range of tests may be affected by biotin supplementation, including those used in the diagnosis or monitoring of cardiac disease, endocrine disorders, malignancies, anemias, and infectious diseases (Table 1).[6]

Biotin-containing blood samples can affect laboratory tests by competing with biotinylated reagents for binding to streptavidin. Depending on whether the assay is noncompetitive or competitive, the result may be falsely low or falsely high (Figure). In noncompetitive or sandwich immunoassays, supplemental biotin competes with reagent biotin for binding to streptavidin-coated beads. With a smaller volume of reagent biotin-streptavidin complexes formed, the assay signal is decreased and a factitiously low result is reported. This is in contrast to competitive immunoassays, which are generally used to measure small molecules such as FT4 or FT3, where the assay signal is inversely proportional to the analyte concentration. In these immunoassays, biotin competes with labelled biotinylated analyte for binding to streptavidin and results can be spuriously high.

In the Holmes study referred to above, 37% of the biotin-based immunoassays evaluated were affected by serum biotin levels of less than 51 ng/mL.[4] Mean peak serum biotin concentrations of 8.6 ng/mL have been reported following consumption of a single dose of 1 mg, while concentrations of 495 ng/mL have been reported following consumption of 100 mg.[4] In a study by Grimsey and colleagues, ingestion of biotin for 5 consecutive days was found to produce peak median serum biotin levels of 46 ng/mL (5 mg dose daily), 103 ng/mL (10 mg dose daily), and 184 ng/mL (20 mg dose daily).[8] The higher the dose of biotin ingested, the more likely that biotin-based laboratory assays will be impacted.

Increasingly, biotin consumption is being found to result in inaccurate laboratory findings that lead to misdiagnosis and mismanagement. Misleading thyroid function results are often described in the medical literature,[2,3,9-13] as biotin causes falsely high FT4 and FT3 values and falsely low TSH results that mimic hyperthyroidism. In one reported case, a newborn female with a positive screening test for congenital hypothyroidism was found to have decreasing TSH levels and elevated FT4 levels on subsequent testing.[12] Further investigations revealed that the neonate had been started on a vitamin cocktail containing 10 mg of biotin daily because the baby’s sibling had died of organic acidosis a few years prior. Discontinuation of biotin supplementation and repeat thyroid function testing using an alternative methodology confirmed the initial diagnosis of hypothyroidism, and thyroxine therapy was initiated.

In another case, a 64-year-old female with end-stage renal disease was thought to have adynamic bone disease due to a low normal parathyroid hormone (PTH) level, intermittently increased serum calcium level, and severe osteoporosis.[14] However, her increased alkaline phosphatase result was inconsistent with the low bone turnover observed in adynamic bone disease. It was later discovered that the patient had been ingesting 10 mg of biotin per day for restless leg syndrome. Repeat testing on a different analytical perform that did not use biotin-streptavidin technology found the patient’s PTH concentration to be markedly elevated, consistent with secondary hyperparathyroidism.

Mitigating biotin interference

While laboratory professionals have been aware of biotin interference for many years, the problem has been amplified recently with increasing use of the supplement. In November 2017 a growing number of adverse events associated with biotin, including one patient death following an incorrect cardiac troponin assessment secondary to biotin interference, led the US Food and Drug Administration (FDA) to warn the public, health care providers, and laboratory personnel that biotin may interfere with certain laboratory tests and cause misleading test results.[15]

It is paramount that health care providers and patients be informed of the potential errors in laboratory results with biotin use. Physicians should always ask their patients about biotin supplementation during history taking. The question should be thoughtfully posed (e.g., “Are you taking any supplement for hair, skin, or nail benefits?”) since patients may not be aware of the ingredients in a supplement, as these are not always listed clearly on the label.

Patients taking biotin should be advised to discontinue the vitamin for at least 1 day before a blood test, or up to a week before testing if high doses have been consumed. The half-life of biotin is dependent on various factors, including the patient’s kidney function and the dose and duration of biotin use. In individuals with normal renal parameters, the half-life of biotin after a single dose of 0.6 mg has been reported as less than 2 hours. In contrast, the half-life following a single biotin dose of 100 mg to 300 mg is between 8 and 19 hours.[4,16]

When patients on biotin require urgent blood work, such as when they present to the emergency department, the ordering physician should consult local laboratory staff. Laboratory physicians can provide information on which particular assays on the test menu may be affected by biotin, the magnitude and direction of interference, and whether some laboratory tests on the same analytical platform are more vulnerable to biotin interference than others. Further, the laboratory physician can arrange for alternative testing using a different methodology not affected by biotin or may be able to request removal of biotin from the sample via pretreatment with streptavidin-coated beads.[6,17]

Fortunately, the results of a recent survey completed by 18 endocrinologists in BC indicate a good understanding of biotin interference (Table 2). However, endocrinology is not the only specialty affected, and further work is needed to ensure information about the impact of biotin on laboratory testing is disseminated to all physicians.

Summary

The case of a 54-year-old female being assessed for thyroid dysfunction demonstrates the harm vitamin supplementation can cause. In this case, laboratory findings erroneously indicated thyrotoxicosis—findings that were eventually determined to be the result of high-dose biotin supplementation when the patient received follow-up testing, and she was ultimately diagnosed as euthryoid.

When found in high concentrations in blood, biotin can interfere with laboratory tests that employ biotin-streptavidin interactions as part of the assay technology. Depending on whether the assay is noncompetitive or competitive, the result may be falsely low or falsely high. Increasingly, biotin consumption is being found to result in inaccurate laboratory findings that can lead to misdiagnosis and mismanagement.

While responses from a recent survey completed by endocrinologists in BC indicate a good level of understanding where biotin interference is concerned, more must be done to ensure that physicians working within and outside the laboratory become familiar with the potential of biotin to interfere with test results.

Competing interests

None declared.

This article has been peer reviewed.

Mr Fan is an undergraduate student at the University of British Columbia. Dr Pudek is the regional medical lead for clinical chemistry for Vancouver Coastal Health laboratories. He is also a clinical professor in the Department of Pathology and Laboratory Medicine at UBC. Dr Mattman is a staff medical biochemist at St. Paul’s Hospital. He is also a clinical associate professor in the Department of Pathology and Laboratory Medicine at UBC and serves as the medical biochemistry discipline lead at BC’s Agency for Pathology and Laboratory Medicine. Dr Dahl is the division head of endocrinology at Vancouver General Hospital and a clinical professor in the Division of Endocrinology at UBC. He is also the current president of the Society of Endocrinology and Metabolism of British Columbia. Dr Wong is the regional medical lead for pre- and post-analysis for Vancouver Coastal Health laboratories, and a clinical assistant professor in the Department of Pathology and Laboratory Medicine at UBC.